THE FIRST U-PB SHRIMP DATING OF ZIRCONS FROM CAPITANIAN (MIDDLE PERMIAN) DEPOSITS OF THE OMOLON MASSIF (NORTHEAST RUSSIA)

U-Pb dating of zircons from two samples of stratotype sections of the Gizhiga Formation of the Middle Permian of the Omolon Massif was first performed. Weighted average ages are 266 ± 2 and 265 ± 3 Ma taking into account the error, are consistent with Capitanian age previously established by paleontological determination. The presence of a detrital zircon population made it possible to identify several sources in the Omolon Basin. Pre–permian zircons are associated with erosion of basement deposits of the Omolon Massif, and the Middle Paleozoic volcanic rocks of the Kedon series and Permian population of zircons linked with volcanic activity of the Okhotsk-Taigonos volcanic arc.

New minimal 87SR/86SR values in biogenic carbonates of the Permian of the Omolon massif (North-Eastern Asia)

For the first time very low values (up to 0,706707) of the ratio 87Sr/86Sr were recorded in the biogenic carbonates of the Omolon massif (Northeast Asia) of the Capitanian age. These results are in good agreement with previously obtained data on limestones in Japan (Kani et al., 2013; 2018). In general, the strontium ratio curve constructed by us repeats the well-known world trend, differing by its somewhat underestimated (by an average of 0,000-0,0008) its values. The Capitanian strontium minimum can be associated with the entry into the ocean of significant amounts of lightweight femic strontium due to a sharp increase in paleospreading. The maximum values of the strontium ratio, obtained from the middle part of the Intomodesma evenicum bivalve Subzone are 0,706986, which corresponds to the upper part of the Wuchiapingian stage.

Late Ladinian to early Carnian radiolarians from the section of Pravyi Vodopadnyi creek, Omolon Massif, North-Eastern Russia

The late Ladinian to early Carnian radiolarian assemblage is found for the first time in the Pravyi Vodopadnyi Creek Section, Omolon Massif, North-Eastern Russia. The assemblage consists of early Carnian radiolarian species that were previously described from sections of Kotel’nyi Island (New Siberian Islands): Glomeropyle aculeatum, G. cuneum and Pseudoeucyrtis annosus, and of species known from the late Ladinian of Dzugadzak Section (Omolon Massif): Glomeropyle algidum and Pseudostylosphaera omolonica. The taxonomic composition (dominance of genus Glomeropyle) indicates high-latitude, boreal nature of assemblage. The taxonomic affinity of coeval radiolarian assemblages of late Ladinian and early Carnian of Omolon Massif and New Siberian Islands gives opportunity for favorable estimation of radiolarian correlation of boreal Triassic.